Table 1: Results for the arsenic speciation in NIST SRM 1568a (rice flour) in μg kg−1. The material is not certified for species, only the total (290 ± 30 μg kg−1, where the ± term is an expanded uncertainty and corresponds approximately to a 95% confidence interval).

Notes. The ± terms are as provided by the researchers. They are predominantly standard deviations for some small number of replicates. Further details are provided in the text. Values have been rounded to the first uncertain digit. The numbers in the “sum” columns may differ from the sums of the numbers presented in the individual columns because of rounding effects. Not all researchers reported values for all four species. No ± terms have been calculated for the sums where this had not been done by the researchers, though clearly this would be possible for many entries. Many of the sample extraction methods did not preserve the redox state of the inorganic arsenic species.